While wearing the Chewbacca costume, Mr. Hat's eyes are in the normal position on his head, not on top of the hat's rim.
The magazine title goes from "Crack Whore" to "Naughty Mom" for a moment, when Chef approaches Stan.
While Kenny is a zombie, his arms are attached in some shots and dismembered on other shots.
In the Mir space station scene, the astronauts are seen with the Dutch flag, instead of the Russian one, on their chest.
In the middle of the fracas with our heroes decapitating zombies, impaling them, and cutting off limbs, with blood spurting everywhere on everyone constantly, Cartman's "ghost" costume never once gets a single blood stain.